Question 1

Which of the following is the correct first step when balancing a redox reaction?

Accepted Answer

Split the reaction into two half-equations: one for oxidation and one for reduction.

Question 2

In the redox reaction between $$\mathrm{Sn$$^{2+}$$}$$ and $$\mathrm{Fe$$^{3+}$$}$$, $$\mathrm{Sn$$^{2+}$$} is $$oxidized to $$\mathrm{Sn$$^{4+}$$}$$ and $$\mathrm{Fe$$^{3+}$$} is $$reduced to $$\mathrm{Fe$$^{2+}$$}. $$Which of the following correctly represents the oxidation half-equation?

Accepted Answer

$$\mathrm{Sn$$^{2+}$$ \rightarrow Sn$$^{4+}$$ + 2e^-}$$

Question 3

When balancing a redox reaction in acidic solution, which step comes immediately after balancing all atoms except hydrogen and oxygen?

Accepted Answer

Balance oxygen by adding $$\mathrm{H_2O}.$$

Question 4

A student is balancing the following half-reaction in acidic solution: $$\mathrm{$$MnO_4$$^- \rightarrow Mn$$^{2+}$$}. $$Which of the following is the correct sequence to balance this half-reaction?

Accepted Answer

Add $$4\mathrm{H_2O} to $$the right, $$8\mathrm{H^+} to $$the left, then $$5e^- to $$the left.

Question 5

Which of the following statements about balancing redox reactions in basic solution is correct?

Accepted Answer

After balancing as if in acidic solution, add the same number of $$\mathrm{OH^-} as$$ $$\mathrm{H^+} to $$both sides.

Question 6

In a redox reaction, the number of electrons lost in the oxidation half-reaction must equal the number of electrons gained in the reduction half-reaction. What is the consequence if this is not achieved?

Accepted Answer

The overall reaction will not be balanced in terms of charge.

Question 7

A chemist is balancing a redox reaction in basic solution and finds $$6\mathrm{H^+} on $$the left side of the equation. What should be the next step?

Accepted Answer

Add $$6\mathrm{OH^-} to $$both sides of the equation.

Question 8

Which of the following best describes why it is necessary to balance both mass and charge in redox reactions?

Accepted Answer

Because redox reactions involve the transfer of electrons, both the number of atoms and the net charge must be conserved.

Question 9

Consider the following unbalanced redox reaction in acidic solution: $$\mathrm{Cr_2O_7$$^{2-}$$ + Fe$$^{2+}$$ \rightarrow Cr$$^{3+}$$ + Fe$$^{3+}$$}. $$What is the correct number of electrons that must be transferred to balance the half-reactions?

Accepted Answer

6 electrons

Question 10

After combining two balanced half-reactions, a student notices that $$4\mathrm{H_2O}$$ appears on both sides of the equation. What should the student do?

Accepted Answer

Cancel $$4\mathrm{H_2O}$$ from both sides.

Question 11

Which of the following is a correct step when converting a redox equation balanced in acidic solution to one appropriate for basic solution?

Accepted Answer

Combine each $$\mathrm{H^+}$$ and $$\mathrm{OH^-} to $$form $$\mathrm{H_2O}.$$

Question 12

A redox reaction is said to be spontaneous if which of the following conditions is met?

Accepted Answer

The change in Gibbs energy ($$\Delta G) is $$negative.

Question 13

In the process of balancing a redox reaction, why is it important to check both the number and type of atoms and the charge on each side of the reaction?

Accepted Answer

To ensure the law of conservation of mass and charge is satisfied.

Question 14

Which of the following is a correct method for balancing oxygen atoms in a redox half-reaction in acidic solution?

Accepted Answer

Add $$\mathrm{H_2O} to $$the side deficient in oxygen.

Question 15

A medical laboratory is analyzing a patient's blood sample and needs to balance the following redox reaction in acidic solution: $$\mathrm{$$ClO_3$$^- \rightarrow Cl^-}. $$Which of the following is the correct number of electrons to add to balance the charge?

Accepted Answer

6 electrons

Question 16

In a historical industrial process, iron(II) ions are oxidized to iron(III) ions. Which of the following half-equations correctly represents this oxidation?

Accepted Answer

$$\mathrm{Fe$$^{2+}$$ \rightarrow Fe$$^{3+}$$ + e^-}$$

Question 17

A student is asked to balance the following redox reaction in basic solution: $$\mathrm{NO_2$^- \rightarrow NO_3$^-}. $$After balancing in acidic solution, the student finds $$2\mathrm{H^+} on $$the left. What should the student do next?

Accepted Answer

Add $$2\mathrm{OH^-} to $$both sides, then combine $$\mathrm{H^+}$$ and $$\mathrm{OH^-} to $$form $$2\mathrm{H_2O}.$$

Question 18

Which of the following is a real-world example where balancing redox reactions is essential?

Accepted Answer

Calculating the correct stoichiometry for reactions in batteries.

Balancing Redox Reactions in Acidic and Basic Solutions

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